Signaling system



May- 12, 1942.

D. K. GANNETTV 2,282,719

SIGNALING SYSTEM Fild Oct. 25, 1940 A5 POLAR/ZED LINEAR DETECTOR- L 42/ LAW DETECTOR lNl/ENTOR "D KGANNETT BY ATTORNEY Patented May 12, 1942 SIGNALING SYSTEM Danforth K. Gannett, Mountain Lakes, N. 3., as-

signor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 25, 1940, Serial No. 362,781

8 Claims.

This invention relates to signaling systems and particularly to systems employing voicefrequency currents for transmitting signals.

Objects of the invention are an increase in the reliability 'ofalternating current signaling and the prevention of false operation in response to interference currents.

In signaling systems in which current of one or more voice frequencies is used for signaling, the signal receiver must respond to signaling cur= rent without being responsive to voice currents or interference currents of signaling frequency. It is known in such systems to employ frequency selective or time delay arrangements for preventing false signal operations.

This invention is a signal device which is operatively responsive to application of signaling currents of sinusoidal wave form and which is operatively non-responsive to currents of other wave forms.

According to one feature of the invention, false signal operation is prevented in a voice frequency signaling system by distinguishing between si naling currents which are of sine wave form and voice currents which have a relatively high peak factor. That is, the ratio of the maximum to the root mean square amplitude of sine wave signaling current is low enough compared with the ratio of the maximum to the root mean square amplitude of voice currents so that this difference may be used to prevent signal operation in response to voice currents.

Another feature of the invention is a signal re ceiver in which the signal relay has a first winding connected by a linear detector to the line over which voice and signal currents are transmitted and a second winding connected to this line by a square law detector, the windings being differentially energized and the relative level of the output of said detectors being so adjusted that the energization of the first winding exceeds the opposite energization of the second winding'by a large enough margin to cause operation of the relay upon the transmission of sine wave signaling current in the line. But when voice currents are being transmitted, either alone or at the same time as signaling current is being transmitted, the energization of the second winding is strong enough to prevent operation of the relay.

A signal receiver arranged in accordance with the invention is shown in the drawing which consists of a single figure. Referring to the draw ing, a signal receiver. SR is connected to a line L over which signals and voice currents are trans mitted.

The signal receiver SR. consists of a transformer T having an input winding ill and two output windings H and i2, potentiometers I3 and it, a linear detector it, a square law detector it, and a polarized signal relay 20. The left winding of relay 2% is connected in the output circuit of the linear detector and its energization tends to operate the relay; while the right winding is connected in the output circuit of the square law detector and opposes operation. The potentiometers i3 and I l are adjusted so that in response to sine wave signaling current the output of the linear detector exceeds that of the square law detector sufficiently to operate relay 20. But in response to voice currents, having a relatively large peak factor, the output of the square law detector is relatively larger compared to that of the linear detector and the energization of the right winding of relay 2!] will prevent its operation. A constant output amplifier may be added between the detectors and the line. The operation of relay 20 responsive to signaling current closes a circuit through conductors 2i and 22 to effect any desired result.

The performance of such a signal receiving arrangement may be analyzed by assuming that the signaling currents have a pure sine wave form and that the voice currents consist of rectangular tion k of a half cycle.

to a sine wave. The characteristics of the two waves are as follows:

Rectangular Sine wave wave Root mean square value hw/TC Peak amplitude- A h Peak factor W 17% Ratio of peak factors -R=j The direct current output of the linear detector is 1 and the direct current output of the square law detector is where g/(a) is the wave applied to the input of the circuit, and 7m and ms are constants related to the sensitivities of the two circuits.

For the sine wave, g/(a) =A sin oz, and

The relay will operate whenever the net operating current exceeds some minimum value. That is, when I L I 0 2A A 711114-3 S It is evident by inspection that the relay operates for a range of values of A lying between the two solutions of the above equation, which are:

arm, Hm? m,

(5) A 2 when 1rm, 1 m? m.

It is generally desired that the device responds 'to a definite range of received currents. Let

;. J Afi It can be shown that this calls for the following relation between m1. and mi:

and

TI, iv- 0 1) Now consider the rectangular wave. In this case Z/(u) =h, [:1 =0 to a =k1r] =0, [a=k1rt0 a=1rl I Q, khm

I1 klflm,

If this wave is to operate the relay, the following condition must be fulfilled:

khm kh m 1 'm 4111.1 w l t 1 ne} This has a real solution only when 47mi kmi Solving for h,

1r 1 i s) which is about unity. With q=9 (about 19 decibels), no false operations will occur if R exceeds about If the peak factor just meets the condition of (10) permitting false'operation, the necessary amplitude of the interference is m 1 0 5 (q +q- The ratio of this to A2, the minimum signal amplitude which will operate the relay, is

when q=4, this ratio is about 2; and when q=9, it is about 4.

From the above, it is found there is a sufficient margin between the output of the linear and square law detectors to enable satisfactory discrimination between sine wave signaling current and voice currents.

The invention is not limited in its application to voice frequency signaling but is generally applicable to any signaling system in which signal operation is desired responsive to sinusoidal signal currents but not in response to currents having some other wave form.

What is claimed is:

1. In a signaling system including a line sub- I jected to voice currents and to signals consisting of voice frequency currents of sine wave form, a signal receiver for responding to incoming signals, said receiver comprising a differential signal relay, two detectors connected in multiple for response to currents transmitted through said line, one of said detectors being a. linear detector and the other of said detectors being a.

square law detector, the output of the linear detector connected to one winding and the output of the square law detector connected to another winding of said. relay, and means controlling the input to said detectors so that the output of the linear detector is enough larger than the output of the square law detector to efiect the operation of said relay in responseto signal currents in said line but is not enough larger to eflect the operation of said relay when voice currents are being transmitted through said line.

2. In a signal device for connection with a line through which voice currents and voice frequency signaling currents of sine wave form are transmitted, a polarized signal relay, a linear detector, a square law detector, an operating winding of said relay connected in the output circuit of the linear detector, a biasing winding of said relay connected in the output circuit of the square law detector, means comprising a transformer for ap-- plying energy from voice and signaling current transmitted through a connected line to both of said detectors, and means for adjusting the relative level of the energy applied to said detectors so that the energization of said operating winding effectsthe operation of said relay responsive to sine wave signaling currents and so that the energization of said biasing winding prevents the operation of said relay responsive to voice currents.

3. A signal device comprising an input transformer, a linear detector, a square law detector,

a signal relay, an operating winding of said relay connected in the output circuit of the linear detector, a biasing winding of said relay connected in the output circuit of said square law detector, and means connecting the input circuits of said detectors to the output circuit of said transformer, the energization of the omrating winding of said relay responsive to the application of signaling currents of sine wave form to said transformer being effective to operate said relay, the energization of the biasing winding of said relay linear detector, another potentiometer connecting said transformer to said square law detector, a polarized signal relay, an operating winding of said relay connected in the output circuit of said linear detector, and a biasing winding connected in the output circuit of said square law detector, said relay and potentiometers so adjusted that the current in the output circuit of the linear detector is enough larger than the current in the output circuit of the square law detector responsive to the application of voice frequency signaling current of sine wave form to said transformer to efiect the operation of said relay and the current in the output circuit of the square law detector is large enough when voice currents are applied to said transformer to prevent the operation of the relay.

6. In a signaling system, the method of selectively distinguishing between currents having a wave form with a high peak factor and currents having a wave form. with a low peak factor, said method comprising rectification of the alternating current to obtain a current the amplitude of which is directly proportional to that of the alternating current, rectification of the alternating current to obtain a current the amplitude of which is proportional to the square of the amplitude of the alternating current, the differential combination of the linear and square law rectified being effective to prevent the operation of saidv relay while voice currents are being applied to said transformer. v

i. A signal device comprising an input transformer, a linear detector, a square law detector, a signal relay, an operating winding of said relay connected in the output circuit of the linear detector, a biasing Winding of said relay connected in the output circuit of said square law detector,

means connecting the input circuits of said detectors to the output circuit of said transformer, and means for adjusting the relative levels of the energy applied to each of said detectors, the output of the linear detector being sufliciently larger than the output of the square law detector responsive to the application of voice frequency signaling current of sine wave form to said transformer to effect operation of said relay, the output of the square law detector being large enough responsive to voice currents to prevent the operation of said relay.

5. A signal device comprising an input transformer, a linear detector, 9. square law detector, 9. potentiometer connecting said transformer to said currents, and the adjusting of the relative am plitudes of the rectified currents to obtain a desired difference between these currents'when the alternating current is of one of said wave forms.

7. In a signaling system, the method of selectively distinguishing between currents having a wave form with a high peak factor from currents having a wave form with a low peak factor, said method comprising rectification or the alternating current to obtain a current the amplitude of which is directly proportion to that of the alternating current, rectification of .the alternating current to obtain a current the amplitude of which is proportional to the square of the amplitude of the alternating current and the differential combination of the linear and square law rectified currents.

8. In a signaling system in which signals are transmitted by alternating current of a sine wave form and in which voice currents and other interference currents having a wave form with a high peak factor are present, the method of obtaining a signal response only when signaling current is being transmitted and substantially no voice current or other interference current is being transmitted, comprising rectification of the alternating current to obtain a direct current which is proportional to the first order of the amplitude of the alternating current, rectification of the alternating current to obtain a direct current which is proportional to the square of the amplitude of the alternating current, the difl'erential combination of the two rectified currents, and the adjustment or the relative amplitudes of the rectified currents so as to obtain a signal response only when substantially all of the alternating current is of sine wave form.

' DANFORTH K. GANNETT. 

